All Coast Guard helicopters had safety check after alert
The Irish Coast Guard's Rescue 116 helicopter was subjected to a safety and maintenance inspection just three months ago.
The revelation came as it was confirmed all five of the Sikorsky S-92A helicopters in the Irish Coast Guard fleet were checked in the wake of a service alert issued by the US aviation giant at Christmas.
Sikorsky issued the service notice after an incident involving precisely the same make and model of helicopter in the North Sea.
In that case, an S-92A encountered what were described as "unexpected control responses" during a routine North Sea shuttle flight on December 28.
The helicopter made an emergency landing on an oil rig helipad - but the aircraft spun on landing causing damage to its rotors and also gouging the landing deck.
No-one was injured in the incident.
All five Irish Coast Guard helicopters were then inspected. The Dublin and Sligo helicopters - both of which were involved in the rescue operation last Tuesday off the Mayo coast - were in the second batch inspected.
The Irish Coast Guard said no issues were raised.
One source said that while nothing was being ruled out at this stage of the Air Accident Investigation Unit (AAIU) probe, it was unlikely the rotor unit was an issue in the loss of Rescue 116.
"In the North Sea case, the helicopter was landed by the flight crew. They were also able to issue an alert over the incident before diverting to a nearby rig helipad for a landing," he said.
However, in the case of Rescue 116, whatever happened was so catastrophic the flight crew hadn't the chance to even issue a mayday. The last contact with the helicopter was a transmission that it was preparing to land for refuelling at Blacksod in Co Mayo.
Seconds later, Rescue 116 vanished from radar and radio contact.
The S-92A boasts an impressive safety record and is now the medium-range search and rescue helicopter of choice for numerous countries, and almost 290 are in service worldwide.
Boasting twin engines, the S-92A is also equipped with an array of safety devices.
However, the same type was involved in a fatal accident in March 2009.
In that case, an S-92A operated by Cougar Helicopters was on a shuttle flight from Newfoundland, Canada.
The helicopter encountered mechanical problems just 30 minutes into the flight after an oil pressure warning light triggered.
The crew was forced to ditch some 50km from St John's.
Just one of the 18 people on board survived.
An investigation by the Transportation Safety Board of Canada (TSBC) found that 16 separate factors were involved in the tragedy.